The thermal management system of an automobile typically utilizes multiple cooling loops, thus providing the desired level of flexibility needed to regulate the temperatures of multiple vehicle subsystems. System complexity may be dramatically increased if the vehicle utilizes an electric or hybrid drive train due to the need to regulate the temperature of the vehicle's battery pack.
FIG. 1 is a high level diagram that illustrates the basic subsystems within the thermal management system 100 of a typical electric vehicle. In general, the thermal management system of such a vehicle includes a refrigeration subsystem 101, a passenger cabin HVAC subsystem 103, and a battery cooling/heating subsystem 105. In an alternate configuration illustrated in FIG. 2, the thermal management system 200 also includes a drive train cooling subsystem 201. Thermal management systems 100 and 200 also include a controller 109. Controller 109 may be a dedicated thermal management system controller, or may utilize the vehicle control system in order to reduce manufacturing cost and overall vehicle complexity.
Refrigeration subsystem 101 is designed to be thermally coupled via one or more heat exchangers to the other thermal subsystems comprising systems 100/200 whenever it is necessary or desirable to reduce the temperature in the thermally-coupled subsystem. As such, in a conventional system the heat exchanger used to couple the refrigeration subsystem 101 to the other thermal subsystems is sized to insure sufficient cooling capacity under maximum thermal loading conditions, i.e., the conditions in which the coolant temperature of the other cooling subsystem(s) is at the highest expected temperature and thermal dissipation requirements are set to the highest possible level. Generally, however, the thermal management system will not be required to provide this level of thermal dissipation. As a result, heat will be extracted from the coolant at a rate much greater than that being input into the coolant by the devices being cooled, leading to a rapid cooling of the coolant and large swings in coolant temperatures between coolant and components, and most importantly large swings in the amount of refrigerant cooling capacity used in reaction to the coolant temperature inside the heat exchanger. In order to avoid such temperature and cooling capacity swings, a conventional thermal management system may regulate the coolant flow rate through the heat exchanger by regulating the coolant pump speed. Alternately, a conventional thermal management system may rely on the self-regulating aspects of the refrigerant thermal expansion valve based on the fixed super-heat setting.
While the conventional approaches of controlling the thermal dissipation provided by the refrigeration system are adequate for many applications, an improved system for controlling thermal loads and thermal dissipation levels is desired. The present invention provides such a thermal management system.